1. Field of the Invention
This invention relates to an image reproducing apparatus. This invention particularly relates to an image reproducing apparatus, wherein a laser beam produced by a semiconductor laser is directly modulated in accordance with an image signal, the modulated laser beam is caused to scan a photosensitive material in a main scanning direction and a sub-scanning direction, and an image represented by the image signal is thereby reproduced on the photosensitive material.
2. Description of the Prior Art
Various image reproducing apparatuses have heretofore been used wherein a light beam is modulated in accordance with an image signal, the modulated light beam is caused to scan a photosensitive material in a main scanning direction and a sub-scanning direction, and an image represented by the image signal is thereby reproduced on the photosensitive material. In such image reproducing apparatuses, semiconductor lasers are often used as light sources for producing the light beams. Semiconductor lasers are advantageous in that, for example, the laser beams produced by the semiconductor lasers can be modulated directly, and the semiconductor lasers can be driven with a small driving electric power.
Basically, such an image reproducing apparatus comprises:
a semiconductor laser for producing a laser beam,
a driving circuit for driving the semiconductor laser,
a main scanning means for causing the laser beam to scan a photosensitive material in a main scanning direction,
a sub-scanning means for moving the photosensitive material with respect to the laser beam in a sub-scanning direction, which is approximately normal to the main scanning direction, and
a modulation means for feeding a modulating signal into the semiconductor laser driving circuit, the modulating signal modulating the laser beam in accordance with an image signal.
For the purposes of causing the laser beam, which has been modulated in the manner described above, to scan the photosensitive material in the main scanning direction and in the sub-scanning direction, a technique is often employed wherein the laser beam is caused by a light deflector, such as a rotating polygon mirror or a galvanometer mirror, to scan the photosensitive material in the main scanning direction, and at the same time the photosensitive material is moved with respect to the laser beam in the sub-scanning direction, which is approximately normal to the main scanning direction. In such cases, for the purposes of defining the timing with which the modulation of the laser beam is begun, it is necessary to detect that the leading end of the photosensitive material, which is moving, has reached the position to which the laser beam is irradiated. Also, for the purposes of achieving horizontal synchronization, it is necessary to detect that the laser beam has passed through a predetermined point (i.e., a main-scanning start point) outside of an effective scanning region with respect to the photosensitive material.
In cases where the semiconductor laser is employed as the light source for producing a reproducing light beam, for the purposes of detecting the leading end of the photosensitive material and the main-scanning start point, a semiconductor laser for synchronization has heretofore been provided independently of the semiconductor laser for image reproduction. A synchronizing laser beam, which has been produced by the semiconductor laser for synchronization and has a predetermined intensity, is caused to impinge upon a single light deflector together with the reproducing laser beam. The synchronizing laser beam and the reproducing laser beam are deflected such that the position, which is being scanned with the synchronizing laser beam, and the position, which is being scanned with the reproducing laser beam, correspond to each other. The leading end of the photosensitive material and the main-scanning start point are detected by detecting the synchronizing laser beam. In this manner, the leading end of the photosensitive material and the main scanning start point can be detected accurately by utilizing the synchronizing laser beam, which has not been modulated.
However, in cases where the semiconductor laser for synchronization is provided in addition to the semiconductor laser for image reproduction, the cost of the image reproducing apparatus cannot be kept low. Also, operations for assembling and adjusting the image reproducing apparatus become complicated.